Telephone system



March 24, 1925.

L. D. KELLOGG TELEPHONE SYSTEM 2 Sheets-She et 1 March 24, 1925.

L. D. KELLOGG TELEPHONE SYSTEM Filed Jail. 51, 1921 2 Sheets-Sheet 2 W277i]? Lang/17K 52/0 -;y

@rzey.

Patented Mar. 24, 1925.

"" "UNITED, STA S AT T QFF LEROY I), xnnnoee, or n-nnnrmnn, iLLmo s, AssIeNon To KELLoeG swIroH- BOARD AND SUPPLYCOMIANY, or cHIcAe I LrnoIs, A conromrrron or ILLI- vTo aZZ whom it may concern:

TELEPHONE SYSTEM.

Application-filed January 31, 1921. sei-iai' No 441.108.

Be it known that I, LEROY D. IQELLOGG, a citizen of the United States of America, and a resident of Deerfield, in the county of Lake and Stateof Illinois, have invented certain new and useful Improvements in TelephoneSystems, of which the following is a specification.

and has to do more particularly with automatic or semi-automatic systems in which switches are used for connecting a calling line to an idle trunk, and an object of my invention is the provision of an improved arrangement which embodies desirable features and advantages all in an efficient, simple and economical manner, and in which the switch of my invention is most positive in its operation. I

A feature of my invention is the provision of a switch of the non-restoring type, that is, one in which thewipers remain in contact with the trunk last used when disconnection is effected, and which will again seize the trunk last used when a call is again initiated, provided the trunk in the meantime has not been seized by another switch and is in use at the time the call is made.

A feature ofmy invention is the provision of a switch of the non-restoring type, which is provided with only three magnets and which has no interlocking mechanism between the magnets; The circuit of this switch is arranged with the so-called' positive drive circuit. I

Another feature of my invention is the provision of switches of the non-restoring type that operate as preselector switches. I also arrange these switches so that they operate as preselector switches under certain conditions and operate as semi-preselectors undercertain other conditions.

A still further feature o-f my invention is the provision of normal or home'contacts for switches of the 11on-restoring"type,'

which normal or home contactsmay be connected in such a manner that the non-restoring switches may or may not rest upon such normal or home contacts. i

Another feature of my invention is the provision of a switch with apositive-drive circuit that doesnot permit'the wipers of the switch to stopon busy contacts nor to pass over idle contacts. The above fea-' tures of my invention, as well as others, will be more fully hereinafter described.

The novel features" of the invention,

through the provision of which the above- 7 mentioned and other advantageous results My invention relates to telephone systems are attained, will be described in'coimection with the accompanying drawings, in

Fig. 1 illustrates diagramma'tically an automatic telephone system including a pair of line switches ofmy invention; 7

Fig. 2 isanother form of line switch em bodying features ofmy invention; and

a Fig. 3 is still another form of line switch embodying features of my invention. f

Figure 4 "shows the construction of the normal or home contacts of some of the switches. i

Referring now more in detail to my inventlon as illustrated in the accompanying dIEtWlIlgS and referring particularly to Fig.

l,t0f'tl18 left thereof I illustrate acalling substation A, which includes the usual talk- 7 ing equipment, with the addition of the call ing device CD. The calling substation A connects at the exchange with theline switch net MM is provided for stepping the wipers 2, 3 and 4: of the line switch B step bystep over the bank contacts 5, G and 7 ofthe switch.

The connector G comprises an impulse relay IR, which relay IR is energized over the line when an idle connector C isseized and is de-energized and energized by impulses from the calling substation A to bring about the primary movement of the w wipers 8, 9 and 10 through the agency of the primary magnet PM. A switching relay SlV isprovidedwhich, when energized,

; line.

connects the secondary magnet SM to be acted upon by impulses from the calling substation A to step the wipers 8, 9 and 10 in a secondary direction over contacts 11, 12 and 13 to engagekcontacts of the called line. A test" relay TRfjfis provided which tests the called line as to its idle or busy condition and, whenbusy,'connects a suitable busyftone from the'busy-back ap paratus BB'to notifythe calling 'subsciibei' as to the busy condition of the calledlh ne ringing control relay RC is provided, whmh connects the ringinggenerator, andfin;

terrupter in circuit to intermittently" apply ringing, current to. the, called .fillbSQT-lbiiis A upervisory re aySRZ- ils'also; provided which is energized when the subs'criber, at the called; substation. answers. Primary off-normal "contacts RON are] provided, which assume their alternate position upon the first stepbfwthe;w pers af nd 10 n primary direction, and shroud: My. n mali o cts: SONJa-realso .prozvlded,

which 21 su 1etheir alternate. picsitiml upon the first step of the wipers 8, 9 and- 1QQiira V p es ne l y R nd acutrofi elay CO and a motor magnetMMFand} arelay 0 n as t ou i h he motor magn MM for providing a positive drive, circuit for the switch. The switch isof the preselector type, in which thewipersqf; the switch are in engagementwithan idle, set of contacts under certain conditions.

Referringto Fig; 3, I- illustrate another form o 1"t. ;li ne switch K of my linvention, comprising a linej relay, LE3, a outwit; relay CO and a motor magnet for advancingthe wipers;

Referring, particularly to the switch B of 7 b this is of the non-restoring. type and is provided w n y hr e na-g et ..a .ne elay,

a motor magnetand acut-ofi; relay, It is to be further noted that this switch is not provided with interlocking; mechanism be. tween the ,difierent magnets, butjthat the magnets are simplemagnets, and control-individual contacts. I 1

- Referringnext to' switch B1101? Rig, 1 and wi e nd; E ssa and These, switches I provide with; normal; or home contacts so that theswitches may, be

li te 0n e pres leetq p r' e p ef.

is Well known that individual switches are generally arranged in groups of 50 or 100, or some such number, and that all these switches have access to trunks that are multiply connected to thebank contactsof the switches. Itfisa further well-known fact thatcertain switches of a group are likely to be used, m re reguently than. other switc es-'1 Tibia cf. are, "i er ect y Vious because "some subscribers "do a great deal-more calling than do other subscribers. ""I'have arranged switches B, G and K so that-when wipers are in connection with-an idle trunk and the trunk is seized by another; switch, the wipers of. all he. s anding r pen the trunk seized y. the: saido her switch, will: be moved from engagement with-the trunk that has 111st; eenjseiz dzaaudih I QVQ K- ltQ engageat; with d runk. However, I have fq mdatliati isne de irab e. Il H lOl necessary to arrange all the switchesina group s9 tha the. Wipers. Q he. same ahvays remainin eigage nent with an idle, trunk (ithus'ope on. the-peselector principle), so -I; h ve, provided, normal or home contactsffor each individual switch. The orma 0 1 111 cont cts re ot mul ipl d.

ew, i -one if. the e wit hes. is ke for use, it is operated to connect to an dle. trunk When he ect on s re ea ed; thewip its Off; he sw tch mmain in engagement with the last trunk used. Now,

iii this, .tru.n1 sseiz d; the Wipers of-Ithesui eh will; step... m. t e" ex e r n and so on: until the, wipers of the switch engage itsnorlnal or home contacts, in which positionfthe wipers-of the switch will; re-

mai-n. until the'switch is again used for callin purpesesr Bu as? ef e s ated,

i e irable, n a. s wh e h w ch is used a great deal, to arrange it so that it; wilL'not. remainin engagement with its meme-1i .1: eme ontacts, t will alw y operateas a preselector, so that the instant that the subscriber, whose, line; is. associated with this switch, removes, his switch, the swit h. mmed ate y; o nec sh trunk to which the wipers are connected.

h t 1 1. .t. .et a he, no mal r h m ooetaetstt witclies Bf, G d; s, s

shown 'in Ei g. 4, The; private wipers of these; switches, have, their end! portions formed into; two separate, contacting portipns g() r(;); and;, 6 4 1; The home or normal contacts :oigtheswitches are likewise formed nt-aw eP l T e;-P9I. II 42 nd 3- he Wipers.v ar pa si g- GI? the ordi r priva e. k contacts b h P iei si fithe W persmay. n agathe pr banknt cta bat When,., y p s ver he normal or, home contacts the-portion 640 the periengag sm contact &2. t; th

same. time, that I the portion,.-6t l-, engages ent qtj h: .Oi: o rse, po i 0 and normal or home contact and, as illustrated,

is of the semi-preselector type, in which the inner or home contact is free from ground so that when the wipers of the switchengage its normal or home contact the wiperswill remain in engagement with the said home contacts until the switch is again put into use for calling purposes.

The line switch G of Fig. 2, as illustrated, is of the full preselector type and is provided with a normal orhome contact, but has connected to its inner contact of the home contact set an interrupter that operates a predetermined period to ground the inner con tacts of the normal or home contacts oi certain switches of the group otswitches, to cause the switches to move their wipers i'rom engagement with their normal or home contacts. a

The line switch K of Fig. 3, as illustrated, is of the full preselector type and is provided with a normal or home contact and has connected to its inner contact of the home contact set a ground to cause the switches to move their wipers from engagement with their normal or home contacts.

:From the above, it is seen that I have by very simple means made non restoring switches preselector switches, and from the above outline it may be seen that the line switch B is provided with a normal or home contact set, which switch operates as a preselector switchwhen its wipers are in engagement with multiple trunk contacts, but which move to their normal or home contacts and remain there until they are used for calling purposes. It is obvious that the switch B may be changed to a switch of the fullpreselector type by grounding the inner contact of its normal or home contact set. Switches G and K are arranged so as tobe full preselector, but it is also obvious that they may be changed to a switch of the semi-preselector type by removing the interrupted ground from the inner contact of the home contact set of the switch G of Fig. 2 and the ground from the inner contact of the home contact set of the switch K of Fig. 3-

From the foregoing it is thought to be obvious that'it might not be desirable to have all of the switches of one group operate on a strictly preselector basis, for the' reason that if practically all the trunks of the group of trunks to which the group of switches have access become busy, it would mean that all of the remaining idle switches of the group of switches would be moved quite frequently as the last few trunks of the remaining trunks were taken for: use.

Having described in general the apparatus as illustrated in the accon'ipanyii'ig drawings, I will now describe in detail the operation of the individual switchesof my invention. Referring now. more particularly to Fig. 1 and assuming that the subscriber at the substation A initiates a call, the removal of the receiver at the calling substation thereat closes. an energizing circuit for the line relay LR of the individual line switch B, traced from battery at normal'contact 15 of motor magnet MM, oveirconductor 16, through the winding of line relay LR, conductor 17, normal contact 18 of cut-oil'relay CO, switchhookcontacts of the calling substation A- and returning through normal contact 19' of cut-ofii relay CO, conductor 20 to ground at normalcontact 21 of motor magnet MM. Wipers 2, 3 and 4 always rest upon a set of contacts 5, t3 and 7 last used, and assuming that the contacts upon which the wipers now rest are busy due to another subscribers line circuit having selected the connector last used by. the subscriber A,

the private contact 5 will be grounded.

Energized line relay LR closes its alternate contacts 22 and 23, and the closing of alternate contact 22 establishes an energizing circuit forthemotor magnetMM, traced from battery through the winding of motor magnet MM, normal contact 24 of magnet MM, conductors 25 and 26, alternate contact 22 of relay LR, conductor 27, normal contact 28 of cut ofi relay CO, conductor 29 and wiper 2 tothe engagedbusy contact 5. The

cut-ofl relay CO is shunted while the wiper 2 is' engaging busy contacts 5 which are grounded. The shunt may be traced from the busy grounded contact 5, wiper 2, conductor 29, normal contact 28, conductor 27, alternate contact 22, conductor 26 to one terminal of the windingof cut-off relay CO,-'and from the other terminal of the cut-01f relay CO, over conductor 30 to ground at alternate contact'23 of line relay LR. A circuit also extends through magnetMM, and cutoff relay CO from battery through the winding of magnet MM,'normal contact24, conductors 25 and 26, through the winding of relay CO, conductor 30 to ground at alternate contact 23 of relay LR. This circuit ust traced has no energizing eflect on the cutoff relay CO at this time due to the shunt about the said relay CO as above tracedjbut whenan idle contact 5 is engaged by the wiper 2 therelay CO will energize over the circuit above traced.

The motor magnet MlVl upon operating steps the wipers2, 3 and 4 into engagement with the next set of contacts 5, 6'and 7. The motor magnet MM upon energization opens its normal contact 24,'*which interrupts its circuit, permitting the de-energization of the said'magnet Should the contacts 5, 6 and 7 now engaged by the wipers 2, .3 and 4 be busy, the motor magnet MM will again. be energized: over the previously. described path,. due to the closure of its interrupter contact 24 and the motor magnet MM will again be energized and de-energized to step the wipers 2, 31am] 4 from one set of contacts 5, 6 and 7 to the next, as long as busy, i. e., as long as grounded contacts are encountered by the private wiper 5. Magnet MM alternately opens andclosesits contact 24, and. thus a vibratory circuit is closed through the winding of cutoff relay CO, as before described, but-due tothe shunt about cut-oft relay CO as before described, .the cut-off relay at this time remains inert. The ground fronithe busy. private contacts 5 encountered by the private wiper 2 extends through the normal contact 24 of motor magnet MM, conductor 31, normal contact 3201 relayCO, conduc tor 33 to the callinglines private normal contacts 11 at the connectors having access to the said calling line to render such con-- tacts. 11 busy. against selection. This ground will be of a vibratory character, and

in View ofthe construction of test relay TR of the connector, the calling, line will. test busy while the. line switch travels, as will be understood from the general operation of the connector. C; The-.motor magnet MM alternately opens and closes; its normal contacts 15 and 21 during; the selecting operation of the individual line switch B, and the interruption of the. contacts 15' and 21 interrupts the energizing circuit. of the line relay LR, but due to. the slowto release construction of the line relay LR, the, said relay isnot affected by the ra id interruptions of the motor magnet and remains energized. 1

. When an idle private contact 5. is encountered by the private wiper 2, the motor magnet MMwill remain unoperated'because the private. contact 5 now engaged-b the pri vate wiper 2 is. free from round. The shunt about the cut-oifrelay 60, as before described during the-selecting operation of the switch, isnow removed and the circuit of the cut-off relay CO is closed over a path which may be tracedfromground at alternate contact 23. of line relay LR, over conductor 3.0, through the winding. of cut-ofl relay CO, conductors 26 and 25, normally closed contact 24 of motor magnetMM to battery and ground: through the winding of motor magnet MM, but the said. motor magnet lWM does not energize over this circuit on account of the resistance of the cut-off relay CO, and it thereforeremains inert.

The opening of normal contacts 18 and 19' of; the cutoff relay CO, upon its. energization, opens the energizing circuit of the line relay LR, but the line relay LR- being oft-he slowrto-release construction is held momentarily energized to hold the initial energizing circuit of the cut-oft". relay closed until a substitute circuit is established. for it, as

will presently be described. Theclosing of alternate contact 32 of cut-off relay CO upon its energization connects ground *over conductor 33 tothe private normalswl l to keep the contacts 11, 12 and 13 busy against select-ion HiltlllllPOIl-t-llk? termination of conversation. The. relay CO having energized, its. contacts 18 and 19 assuming their alternate. po-

sitions, the wipers 2, 3 and 4 of the individual switch B are. now connected. to the contacts 5, 6 and? of the idle connector C, thus extending the calling line to the seized idle connector C. A circuit is. established for the impulse relay IR of the connector C, traced from battery through lefthand winding of relay. IR, contact. 6, wiper 3, a1-

ternate contact 18 of relay CO, through substation A, back through alternate contact 19 of relay CO, wiper 4, contact 7, to, round through the right-hand windingbf relay IR. The closing of alternate contact 40 of the impulse relay IR establishes an energizing circuitfor the relays 41 and 42,.the circuit of relay 41 extending from battery through the right-hand winding of relay cuit for itself, traced from battery through 1 the right-hand winding of relay 41 to ground at its alternate contact 50 of relay 41 The closing of alternate contact 40 of relay IR establishes'a substitute energizing circuit for therelay C0 of the line switch B before it has time to de-energize, which may be traced from battery through the winding ofimagnet MM, its normal contact 24, conductors 25 and 26, through the winding of relay CO, its alternate contact 28,

conductor 29, wiper 2, contact 5, conductors, 45 and 46 to ground at alternate contact 40. of the impulse, relay IR. Magnet lVHVLdoes not operate over this circuit for reasons as before described, andthe said cut-ofi" relay CO remains energized until upon the termination of conversation.

The. energization of relay IR I having brought about. the energization of relays 41 and 42, as already-described, assuming that the called subscribers number at substation D is 45, the subscriber A now operates his calling; device CD to. send four impulses of current, over the line. These four impulses bringabout four de-ener izations-andphergizations of the relay I causing the primary magnet PM "to energize and de-ener-- gize four times to step the wipers 8, 9 and 10 of the connector in a primary direction to the fourth group of contacts, that group containing the contacts of the called line. The circuit of the primary magnet PM may be traced from battery through the' winding of the said magnet PM, normal contact 51 of switching relay SW, conductor 52-, alternate contact'53 of relay 42, normal contact 49 of relay IR, conductor 46, conductor 45, and normal contact 44 of the primary offnormal contacts PON to ground at alternate contact of relay 41.

After the contact 44 of the primary offnormal contacts PON has moved to its alternate position on the first step of the switch shaft, the ground fed from normal contact 54 of relay 55 is substituted for the ground fed through contact 50 of relay 41. After.

the last impulse of the series" has beensent, the steady flow of current through both windings of relay 42*causes the said relay 42, due to its differential action, to neutral ize and restore its contacts to normal. Relay 42 does not restore during the sending of impulses due to its adjustment, construction and the rapidit of the interruptions'of contact 49. It will be noted that the relay 42 when first energized had its upper winding immediately energized by contact 50 of relay 41 andgwas in a neutral condition with its armature retracted when relay IR sent the first impulses, but immediately energized.

when relay IR opened the circuit through the lower winding of relay 42. The closing of normal contact 56 of'relay 42 brings about the energiz'ation of theswitching relay SlV bycurrent traced from battery through the winding of said relay SW, its make-before break contact 57,-norlnal contact 58 of secondary off-normal springs SON,'conductor 59, normal contact 56 of relay 42,'and con} ductor 60 to ground at alternate contact 61 of primary ofi-normalcontacts PON, the

said primary off-normal contacts PON having been moved to their alternate position on the first step of the wipers 8, 9 and 10 'relay CO, conductor 112, bank contact 11,

wiper 8,conductor 66, normal contact 65 of relay TR, conductor .70, normal contact 71 magnet SM operative so that when the callof the connector switch 'ofi' normal; The closing ofalternate contact 51' of the switching relay SWnow renders the secondary ing subscriber at the substation A actuates his calling device CD again to send the last set of impulses, which we haveassumed are five in number, the said magnet SM will be energized and de-energized bythe impulse conductor 46, conductor '45, and alternate and 10 in a secondary directionto engage contacts 11, 12 and 13 of the called line.

Upon the first impulse of the last set, the relay 42 again energizes to permit the sec ondary magnet SM to be operated, and aft-er the last impulse the relay 42 is again deenergized, as, previously described. The

restoration of the relay 42 closes acircuit for the test relay 'IRf'traced from battery through the winding of the said relay, con ductor 63,the alternate contact 64 of relay SW, alternate contact 58 of the secondary off-normal contacts SON (said contacts having been moved to their alternate position upon the first step of the wipers in their secondary direction), conductor 59, normal contact 56 of relay 42, conductor60 to ground at alternate contact 61 ofthe'primary offnormal contacts PON. The closing of alternatecontact 65 of relay TR connects the said relay overconductor66 to the test wiper 8;, and should the called line be busy the private contact 11 of the called line would be grounded, thus closing a locking circuit for the said relay through the private Wiper,

Ualled Zine idle.

Assuming that the called line is idle, prirelay TR opened the circuit of the switching relay SW. The relay SW de-energizing,

opens the circuit forrelay TRat its contact 64, leaving the relayTR dependent upon the potential found upon. the private contact 11 of the called linefor its holding potential, and, as assumed,- this contact is free from ground potential; therefore, the relay TR de-energlzes and returns to normal." The relay TR de-energlzlng causes theenerg1zation of the relay55 over a 'circuitwhich may be traced frombatter through the winding of motor magnet M conductor 110, normal contact 111 of cut-ofl of relay SW, conductor 72, through the lower winding of the relay 5 5, and conduc tor 73 to ground at alternate contacts 74 of relay 41. The closing of alternate contact 7 5 of relay 55-sl10rt-circuits the lower winding of the'said relay, and the closing of al-' ternate contact 76 of relay 55 closes a circuit through the upper winding'of the sald relay, through'the'alternate contact 76 and conductor73to ground at alternate contact 74 of relay 41., The motor magnet MM of the lineswitch B associated with the called of line switch l3,

line is energized Over this circuit and remains energized iuntil conversation has terminated. '5

The closing of alternate contact 77 of relay connects the interrupter I to the relay 78and the circuit forrelay 7 8; may be traced from battery through the winding of the said relay '78, conductor '79, alternate contact 77 of relay 55, conductor 80, normal contact 8110f relay RC and throu h the interrupter I to ground. The relay (8 is thus intermittently energized and de-energized by the rotating interrupter Land upon. each de-energization of the relay 78 the ringing generator RGis connectedto the called line over a circuit extending fromthe ungrounded pole of thegenerator RG, throughnormal contact 82015 ringing control grelay RC, conductor 83, alternate contact 84 ofrelay..55, conductor 85, normal-contact 86 of relay 78, wiper 10, bank-contact -13, through the con denser and call bell of the called substation I), back through bank contact 12, wiper 9, normal contact 87 ot'relay 378, and. conductor ground at alternate contact 54 of relay 55.

Thecall bell of the called subscriber at the substation D is thus intermittently rung, due

to the energization and de energizationoiv the relay 78 by .the interrupter I. When the called subscriber answers and the relay 78 is in its energized position, a circuit for the relay SR is closed, which may be traced from battery through the lower winding of the relay SR, through alternate contact 86- of relay78, wiper 10, contact 18, through the nowclosed contacts of the, substation switchhook at the called substation D, back closing of alternate contact 91 of relay RC closesa lockingcircuit for the said relay RC which may be traced. from battery through the winding of thesaid relay, its alternate contact 91 and conductor 60 to ground at alternate contact 61 of the primary oil'- normal contacts PON. The opening of normal contacts 81 and 82 upon theenergization of relay RC disconnects the interrupter I and the. ringing generator RG to prevent further application of ringing current. 'A, substitute circuit for the relay 7 8 is nowestablished, which may be traced from battery through the winding of the relay 78, conductor 79, alternate contact 77 of relay 55, conductor 80, alternate contact 81 0f relay RC, and conductor '60'to ground. at al ternatc contact ,61 r primary i a contacts PON. The subscribers are new in conversational circuit, and thetalkingcircuit may be traced over theheavily marked conductors,said conductors having the condenser-s K and K interposed.

The subscribers, haying finished conversation, and assumingthatthe subscriber at the calling substation A is first .to replace his receiver upon-the switchhook, the opening of the s'witchhook contacts brings about the de-energization of the impulse relay IR of the connector 1.0. The restoration of the rela IR brings about the o ening of the holding circuit ,of'the "relay Oof the individual switch B, which relay -CO restores and places the individual switch B in condition to be used in establishing another connection.

'The subscriber ,D restoring his receiver upon its iswitchhook interrupts the circuit of .therelay at the switchhook contacts,

causing the said relay to Cloenergize. The

4L1 closes, an-energi-zing circuit for thesecond' ary magnet SM, which may be traced from battery through thewi-nding of said second ary magnet SM, conductor 100, normal contact 99v of relay 41, alternatevcontact 101- of the primary off-normal contacts PON, through the interrupter I to ground. The

secondary magnet SMthus steps the wipers S, 9and' 10xbeyond the last set-of contacts in the groupand the Wipers then restore to normal, from this position by spring tension.

The restoration of the. relay 41 brings about the opening of the-circuit otthe relay 55 at alternate contact 74, and the relay restoring opens the circuit of relay $8 and contact 77 of relay 55-, and the -primaryoflmormal contacts PON having; restored upon the restoration of theswitch.v the opening otthe alternatecontact 61 0t PON brings. about the cle-energizationiioithe relay RC. The

relay .41 also brings about the desenergi zation of the; motor magnet MM of the line switch B :whi'oh is associated with. the called subscrilmr D. All-the apparatus used in establishing .a connection between a calling -subscriberat thesubstation. A and the called subscriber atthe substation Dis now, use in est-ablishat normal and available for ing other connections. 1

Assuming now thatthe subscriber at the called substation D was. first to replace his:

receiver; upon ,thie-switchhook, the openingof the 'switchhook contacts at the substation D brings about the de-energizatio-n of the relay SR. Nothing else happens at this time as the relay IF. still maintained energized over the line of the calling substation A. The callingsubscriber at the substation A replacing his receiver interrupts the circuit of the impulse relay IR atthe switchhook contacts. The relay IR (ls-energizing closes a circuit for the lefthand winding of relay 41, causing the said relay to de-energize, as hereinbefore described. The restoration of the individual switch B and connector C is the sameas previously described from this point on. Should the called subscriber D tail to replace his receiver upon the switchhook after the conversation is terminated, the replacing of the receiver at the substa tion A brings about the de-energization of the impulse relay IR of connector C, the same as before, and the opening of alternate contact 40 of impulse relay IR opens the circuit of the relay C0 of individual switch B, as before described, and causes the releaseof switch B. v

The subscriber at the called substation failing to replace his receiver, permits the continued energization of the relay SR, thus holding the contact of said relay in its alternate position, preventing the difiterential wound relay 41 from restoring to normal and closing the energizing circuit for the secondary magnet The relay 42 energizes when the line relay IR drops back but is immediately restored to normal due to the closure of an energizing circuit through the lower winding of the said relay 42, which may be traced from battery through the said lower winding, conductor 47, alternate contact 95, connector 98, to

ground at normal contact 40 of the now restored impulse relay IR. Relay 42 being differentially wound, restores to normal, and the closing of normal contact 102 of the said relay 42 places a ground upon the private contact ofthe connector C over a circuit tact 5. The placing of this busy potential upon the private contact prevents any individual switch B from engaging the contacts of this busy connector.

If the private contact 5 engaged by the wiper 2 i's idle when the subscriber at the calling substation A initiates a call byre moving his receiver, the line relay LR will energize over a path as before described and operates to close its alternate contacts 22 and 23. i There being no ground on the" private contact 5 'engaged'by the wiper 2,

no shunt will be closed about the cut-off .relay as. before described, and themotormagnet MM will also remain inert due to the groundless pllVfLiJflCOlltlCt 5, and the wipers 2, 3 and 4 Will'rcmain in engagement 1 with the contacts5,6 and 7 that were last i used by the individual switch B in establishing a previous connection. The cut otf relay CO is therefore immediately energized from battery through the motor magnet NLM and cut-off relay CO to ground. at alternate contact 23 of slow-to-release "relay LR and the operation of the circuit from this point on. is the same as previously described.

Thus, it may be seen that the individual switch B only travels when its wipers 2, 3

and 4 are in engagement with. a busy trunk when acall is initiated.

Should the substation A be seized as a called line by a connector engaging contacts 11', 12 and 13, round will be extended to the prlvate contact 11' from the con-1' 21 so that when the subscriber at the substation A removes his receiver as a called subscriber from its switchhook, no energizing circuit isestablished for the line re-.

layLR'due to the opening of normal contacts 1'5 and'2l of motor magnet MM, and this energization of the said motor magnet MM removes the substation control of the line switch B when the substation A is a called line.

, Called me busy.

Assuming now {that the called line is busy, the operation of the circuit is the same up to and including the time that the relay TR momentarily energizes. I The line being busy, the private contact 11 has a busy ground potential placed upon it, thus closing a locking circuit for thetest relay TR from battery through the winding of the said relay, its alternate contact 65, con

ductor 66, and the wiper 8 to ground at contact 11. Theclosing of alternate contact 104 of the test relay'TR connects the busy signal BB to the line to transmit a busy signal to said calling subscriber at substation A, thus notifying him of the busy condition of the said called substation D. The relay TR upon looking to ground at the private contact 11, closes a circuit for relay RC, traced from battery through the winding of relay RC, make before-break contact 89, normal contact 90 of relay SR, normal contact 64 of rel-av SW, conductor 63. alternate contact 65 of relay TR, and conductor 66 to the grounded at alternate contact 61 of the ofi normal contacts PON. Now, should'the' line called be come idle during the time the busy signal is being transmitted to the calling substation, the falling back of relay TR will not cause the called subscriber to be signaled, owing to the fact that relay RC is locked up to ground at contact 61. The calling subscriber now replaces his receiver, bringing about the tie-energization of the impulse relay IR. The relay IR restoring, opens the circuit of the relay C0 of the individual switch B to place the switch in condition for establishing other connections as previously described. The relay IR de-energizing brings about the restoration of the relay 41, due tolthe fact that the relay SR has not been energized. The closing of the circuit through" the left-hand winding of the circuit 41 brings about the neutralization of said relay 41. The closing of normal contact 99 of the said relay 11 closes a circuit through the secondary magnet SM, which magnet steps the wipers 8, 9 and 10 beyond the last set of contacts. The wipers then restore to normal by spring tension. The primary off-normal contacts PON and secondary off-normal contacts SON are also restored, and the apparatus used in this busy connection is now at normal and available for use in establishing other connections.

Operation of suiitch B.

The substation D terminates at the ex change in a line switch B, which is of the non-restoring type. The line switch B is provided with wipers 118,119 and 120 for engagement with its bank contacts 115, 116 and 117. The switch B is provided with a normal or home set of bank contacts 115 115 116, and 117. line switch B be used as a semi-preselector, then the home, bank contact 115 is not connected to ground, but if it is desired that the line switch B always operate asa preselector, then the bank contact 115 is connected directly to ground or through an interrupter to ground as shown in Fig. 2.

1 hen the line switch B operates as a semipreselector. its wipers, whenever left in engagement with a multiple bank contact, will be moved from engagement with this con tact as soon as the trunk is seizedby another switch. This operation will continue to happen until the wipers of the switch are stepped to the normal or home set of the bank contacts 115, 115 ,116 and 117. The motor magnet of the switch B is used not only to advance the switch wipers, .but is If it is desired that the also used as a cut-otl relay when the substation D is a called substation. Assuming now that the subscriber at the substation D initiates a call and that the wipers 118, 119 and 120 are in engagement with the normal'home contacts. 115, 115 116, and 117 (the switch B operating as a semi-preselector), the removal of the receiver at the substation D closes an energizing circuit fol-the line relay LR, traced from battery through the normally closed contact 121 of the motor magnet MM, through the winding of the .line relay LR, conductor 122,normal contact 123 of cut-oft relay CO, through the now closed contacts of the substation switchhook, and back through normal contact 124: of the relay CO, conductor 125 to ground at normal contact 126 of the magnet MM. The line relay LR" energizes over this circuit, and having assumed that the wipers 118, 119' and 120 are engaging its set of normal home n n-multiple contact-s 115, 115 116 and 117 in the bankof contacts of the line switch B, the closure of alternate contact 127 of the line relay LR establishes an energizing circuit for the relay 128, traced from battery, through the winding of the relay 128, conductor 135, normal contact 134 of thernotor magnet MM, conductors 133 and 132, normal contact.13 1 of the relay CO, conductor 130, wiper 118, normal home contact 115, conductor 129, to ground at alternate contact127 ofthe line relay LR. The relay128 upon energizing closes its alternate contact 136,-establishing an energizing circuit for the motor magnet MM, traced from battery through the windingof the motor magnet MM, conductor 110, to

ground :at alternate contact 136 of the relay 128. The motor magnet MM upon operating steps the wipers 118, 119 and 120 from the normal home contact 115, 115 116 and 117 into engagement with the next set of contacts. The -motor magnet MM upon energization opens its normal contact 134, which opens the energizing circuit of the relay 128. and the relay 128 upon de-energization opens its alternate contact 136, which. opens the energizing circuit of the magnet MM. Should the set of contacts now en:

gaged by the wipers be busy, the relay 128 thus alternately energized and de-energized to cause the motor magnet MM to step the wipers 118, 119. and 120 from one'set of contacts 115, 116 and 117 to the next as long the contacts 121 and 126. The grounded alternate contact 136 of the relay 128 also extends over conductor 110, normal contact 111 to the private normal contacts 11 of the connectors which have access to the line D to render said contacts busy against selection.

switch B a shunt is closed about the cut-oil relay CO, the shunt extending from ground at alternate contact 127 of relay LR to one terminal of the Winding of relay CO and the ground encountered by the wiper 118 in engaging busy grounded contacts 115 extends over conductor 130, normal contact 131 and over conductors 132 and 133 to the other terminal of the winding of relay CU. Upon the de-energization' of motor magnet MM, the circuit is closed for the cut-off relay CO from battery through the winding of the relay 128, conductor 135, normal contact 134 of magnet MM, conductor 133, through the windingot' the relay CO to ground at the alternate contact 127 of the line relay LR, but relay CO does not energize at this timeover thisvibratory circuit due to the shunt about its winding, as above described. When an idle contact 115 is encountered by the wiper! 118 no energizing circuit is established for the relay 128 as the contact 115 now engagedis free: from ground, and the relay 128 restoring its alternate contact 136 is opened, preventing further actuation of the motor magnet MM and the shunt is also removed from about the cut-off relay CO. As contact 115 is free from ground, the closingof normal contact 134 of the magnet MM establishes a circuit for the cut-off relay G0, which may now be traced from battery, through the winding of the relay 128, conductor 135, normal contact 134 of magnet MM, conductor 133, through the winding of the relay CO to ground at alternate contact 127 of line relay LR. The cut-oil relay CO energizes over this circuit, but due to the resistance of the relay CO relay 128 is not energized over this circuit. The cutoff relay CO upon energizing opens its normal contacts 123, 124 and thus interrupts the energizing circuit of the line relay LR, but the line relay LR being slow to release is held momentarily ener ized, after its circuit is interrupted, to maintain the circuit of the cut-off relay CO closed until a substitute circuit is established for it. The relay 128 upon de-energization and the relay CO upon energization remove the busy ground from the contacts 11, but the closing of alternatecontact'lll of the cut-oil relay CO connects ground tothe contacts 11, keeping them busy until termination of conversation. The relay CO hav- 7 ing energized, its contacts 123 and124 assume their alternate positions, and the wipers 118,119 and 120 of the'indiv'idua'l switch B are now connected to contacts 115,

116 and 117 of an idle selector or connector, as-the case may be, and a substitute circuit for the cut-oil relay CO is now established over circuit traced from battery through the winding of the relay 128,conductor 135,

g normal contact 134 of the magnet MM", con- During the selecting operation ot the ductor 133, through the winding of the relay CO, alternatecontact 1310f relay CO, conductor 130, wiper 118, contact 115 to ground at the selector or connector, as is readily apparent from the previous description.

It the wiper 118 is in engagement with a contact 115 other than the normal home con tact associated with the substation D, when the subscriber at the substationD initiates a call the line relay LR is energized as before described and operates to close its alternate contact 127, but as there is no ground on the private contact 115, no energizing circuit is established for relay 128, and the relay 128 remaining inert its alternate contact 136 remains open, preventing an energizing circuit bein established from the motor magnet MM and the wipers 118, 119 and 120 therefore remain in engagement with the contacts 115, 116 and 117'. The cutoil relay CO is therefore energized imme diately over circuit from battery through relay 128, to the cut-0d relay CO and to ground at' alternate contact 127 of the line.

relay LR, and the operation of the circuitfrom this point on is the'same as above described.

Assuming that the substation D is neither a called or a calling line and the wipers 118, 119 and 120 are resting in engagement" with an idle set of contacts 115,116 and 117, and assuming that this set ofcontacts are appropriated by another line switch during the time that the subscriber at the substation D is neither calling nor being called, the ground placed upon the contacts to render them busy extends through wiper 118,over conductor 130, through normal contact 131, conductors 132 and 133, nornormal to prevent further actuations of motor magnet MM. From the above description it may be seen that the line switch B, as illustrated and described, is of the non: restoring semi-preselecting type.

Assuming that-the switch B is to operate as a strictly 'preselector, the home contact 115 is connected'to ground, either directly or through an interrupter, now when the wiper 118 engages this ground a circuit is immediately closed for relay 128, which re lay energizing closes a circuit for magnet MM. The operation of magnet MM moves the wipers to the next set of contacts.

From the foregoing it is believed to be apparent that when the home contact 115 is connected to ground the wiper 118 always rests in engagement with a non-grounded contact 115 connected to an idle trunk, thereby maintainingthe wipers of the switch in engagement with an idle trunk so that as soon as the subscriber removes his receiver his line is immediately connected to an idle trunk.

, Operation of switch G.

Referring now to Fig. 2, I show a sub station Fterminating in the main exchange in a line switch G of the non-restoring type. The switch G, as beforementioned, is provided with a set of wipers 154, 155 and 156 for engagement with bank contacts 151, 152

and 153. The switch Gr, like the switch B, is provided with a set of normal or home contacts 151, 151 152 and 153', and if it is desired to operate the switch Gr as a semi-preselector,the normal or home concontact 151 is left disconnected from the source of current, while if it is desired to operate the switch G as a strictly preselector the normal or home contact 151 is connected either directly to ground orto ground through an interrupter. In Fig. 2 I have shown the bank contact 151 connected through an interrupter 900 to ground. 11 the switch G is operated as a' semi-preselector after it is used for extending a call from the substation F, the wipers rest in en a ement with the last set of contacts used until this set of contacts istaken for use by another switch of the group of switches to which switch G belongs. As soon asthisoccurs, the wipers aremoved from engagement with this set of bank contacts and they continue to rotate as long as busy contacts 151 are engaged by wiper 154, until the normal or'honie contact is reached, in which position the switch remains at rest until substation F initiates a further call. If the switch G is operated on a strictly preselector basis, then as soon as the wiper 154 is moved to the home contact 151 the motor magnet MM of the switch will be operated to stepthe wipers to the next set of contacts if the contact 151 is connected directly to ground, or the wipers will remain in engagement with the normal or home set of contacts until the interrupter 900 grounds contact 151 at which time the wipers will be moved from engagement with the normal or home set of 0011- tacts and into engagement with contacts representing an idle trunk. From this it will be seen that the switch Gr may be operated as a semi-preselector or as a preselector.

Assuming that the substation'F initiates a call and that the wipers 154, 155 and 156 are in engagement with the normal home contacts 151, 151 152 and 153 (switch operating as a semi-preselector), the romoval of the receiver at the substation closes an energizing circuit for the line relay LE traced from battery through the winding of said relay, normal contact 157 of cut-off relay CO through the substation, and back to ground at normal contact 158 of the cutoff relay CO Theline relay LE energizes over this circuit, and having assumed that the Wipers are in engagement with the set of normal-home contacts 151, 151 152' and 153, the closure of alternate contact 1.59 of the line relay LE establishes an energizing circuit for the relay 150, traced from battery through the winding of the said relay 150, normal contact 160 of motor magnet MM conductors 161 and 162, normal contact 163 of cut-off relay CO conductor 164, wiper 154, the private home contact 151, conductor 165 to ground at alter-' nate contact 159 of the relay LE The relay 150 upon energizing closes its alternate contact 166, establishing an energizing circuit for the motor magnet M14 from ground at alternate contact 166, to battery and ground through the winding of the motor magnet MM The motor magnet MM upon operation steps the wipers 154, 155 and 156 from the normal home contacts upon which the wipers are resting, into engagement with the next set of contacts. The motor magnet MM upon energization opens its normal contact 160, which opens the energizing circuit of the relay 150, and'the relay 150 upon de-energization opens its alternate contact 166, which opens the energizing circuit of the motor magnet MM? Should the set of contacts now engaged by the wipers be busy, the relay 150 will energize from ground at the busy contact 151 engaged by the wiper 154, over conductor 164, through normal contact 163 of the cutoil relay CO to battery and ground through the winding of relay150 over the previously described path; The relay 150 upon energization in turn again closes an energizing circuit for themotor magnet MM and the relay 150 and motor magnet MM are thus tacts 168 of the connectors, which have ac cess to the substation F, to thus render the said contacts busy against selection. During the selecting operation of the switch G a shunt is closed about the cut-oil relay 00 the shunt extending from ground at alternate contact 159 of the line relay LE over conductor 167, to one terminal of the winding of the cut-01f relay CO and the ground encountered by the wiper 154 in engaging busy contacts extends over conductor 164 co-normal contact 163, to the other terminal of the winding of cut-ofi' relay CO Upon each de-energization oi the motor magnet Mi /1 a circuit is closed for the cut-off relay CO from battery through the winding of relay 150, through normal contact 160 of motor magnet MM through the winding of the cut-oh relay CO and over conductor 167 to ground at alternate contact- 159 of line relay LE The relay CO does not energize at this time over this vibratory circuit due to the shunt about its winding, as above described. When an idle contact 151 is encountered by the wiper 154, relay 150 will restore and contact 151, now engaged, will be free from ground, and the opening of its alternate contact 166 prevents further actuation of the 1notor magnet MM and the shunt is also removed from about the cut-0E relay CO As the contact 151 is free from ground, the closing of normal contact 160 establishes a circuit for the cutoff relay 00 which now may be traced from battery through the winding of the relay 150, normal contact 160 of magnet MM through thewinding of the cut-off relay CO and over conductor 16?, to ground at alternate contact 159 of the line relay LE The cut-oil relay CO energizes over this circuit, but due to the resistance of the cut-oil relay CO relay 150 is not energized over this circuit. The cut-off relay CO upon energization, opens its normal contacts 157 and 158, and this interrupts the energizing circuit of the line relay LE and the line relay LE .de-ener-- gizing opens its alternate contact 159, which opens the initial energizing circuit of the cut-off relay CO ,but the cut--01? relay CO heing slow to release is momentarily heaenergized after the de-energization of the line relay LE until a substitute circuit is established for it from ground over the seized trunk, as described in connection with Fig. 1. This holding ground for the cutoli" relay CO extendstrom the engaged contact 151' of wiper 154, over conductor 164, through alternate contact 163 of cut oil relay CO conductor 167, through the winding of the cut-oil relay CO normal contact 160 of the motor magnet MM to battery and ground through the winding of the relay 150, the cut-off relay CO thus remaining energized until the. termination of conversation. The ground for making switch G inaccessible during conversation also extends over conductor 167 to the connector contacts 168, keeping them busy until termination of conversation.

If the wiper 154 is in engagcn'ient with a contact other than the normal home contact, when the subscriber at substation F initiates a call the line relay LE is ener gized as before described and operates to close its alternate contact 159, but as there is no ground on the'private' contact 151 no energizing circuit is established for relay 150, and the relay 150 remaining inert its alternate contact 166 remains open, preventing an energizing circuit being established for the motor magnet MM, and the wipers 154, 155 and 156 therefore remain in engagement with the contacts 151, 152 and 153 that were last used by the switch G in establishing a connection. The cut-off relay CO is therefore energized to ground at alternatecontact 159 of the relay LE and the operation of the circuit from this point on is the same as above described.

Assuming that the substation F is neither a called nor a calling line and the wipers 154, 155 and 156 are resting in engagement with an idle set of contacts 151,. 152 and 153, and'assuming that this set of contacts are appropriated by another line switch during the time that the subscriber at the substation F is not being called or is not call ing, the ground placed upon the contact 151 to render it busy extends through. wiper 154, conductor 164, normal contact 163 ofthe cut-off relay CO conductors 162 and 161, normal contact 160 of the motor magnet MM to battery and ground through the winding of the relay 150. The

[relay 150 upon energizing closes its alternate contact 166, establishing an energizing circuit for the motormagnet Mil/1 andthe motor magnet MM upon energizing steps the wipers 154,155 and 156into' engagement with the next set of contacts, and continues to do so until an idle set of contacts 151, 152 and 153- are encountered or the home contacts areengaged.

Assuming that the commutator 900 is connected to home contact 151 should the wipers'154, 155 and 156 he stepped into engagement with the normal home contacts, the wipers remain in engagement with the said contacts as long as the brushes of the commutator are engaging insulated portions of the comn'iutator, but when the live segment of the commutator engages the commutator brushes, ground is connected through the live segments thereof and through the wiper 15%, over conductor 16 1, to battery and ground through the winding of the relay 150. The relay 150 upon energizing closes an energizing circuit for r the motor magnet- MM and the motor magnet MM steps the wipers from the normal home contacts into engagement with the next set of contacts, and should thesecoir tacts be busy the wipers continue to be stepped around by the alternate energizer-- tion and de-energization of the relay 150 and motor magnet MM until an idle set of contacts are encountered. a

When the switch G is used for called purposes and when a connector switch applies ground to the private normal contact 168, the cut-off relay CO is energized over a path extending from battery through the winding of relay 150, contact 160 of motor magnet MM and the winding of relay CO to the private normal contact 168. The relay CO energizes, disconnects ground and battery from the subscribers line F, there by removing the substation control of switch G. The relay CO energizes in series with the relay 150, but the relay 150 remains inert when included in this: energizing circuit, for the reasons heretofore assigned.

Operation of switch 1i.

Referringnow to Fig. 3, I show a substation H terminating 1n the mam exchange in a line switch K of the non-restoring type.

The line switch K is provided with a set of wipers 178, 179 and 180 for engagement with the set of bank contacts 175, 176 and 177. The switch K, like switches B and Gr, is provided with a set of home contacts 175, 175 176 and 177. The home contact 175 may either be connected to ground or through an interrupter to'ground, or there may be no connection whatever to this contact. The normal or home contacts as mentioned in connection with switches B and G are non-multipled, but are individual to the bank of contacts individual to switch K. It home contact 175 is connected directly to ground or through an interrupter to ground, the switch will operate on a strictly preselector basis, while if there is no connection to contact 175 the switch operates on the semi-preselector basisthat is, the switch will operateas a preselector as long as itswipers are in engagement with bank contacts connected to trunks, but will not operate as a preselector when its switch wipers are in engagement with its normal or home set of contacts. I have shown the contact 17 5 free from ground connection.

tact 185 of thefmotor magnet MM are in engagement with the normal or home set or contacts 175, 1(1), 176 and 177, and that the switch It IS operated as a semi-preselector, the removal of the receiver at the substation closes an energizing c1rcu1t for the line relay LE traced from battery at normal contact 181 or the motor magnet MM through the winding of the line relay LE conductor 182, normal Contact 183 of the cut-off relay CO through the substa-' tion, back through normal contact 184; of the cut-oft relay CO to ground at normal con- The energization of relay LR closes a circuit for magnet MM extending from battery through said magnet, normal contact- 186, contact 192, wiper 178, home contact175 and contact 190 of line relay LE to ground. Magnet MM energizes and de-energizes, moving the switch wipers, and continues to dose as long as wiper 178 engages grounded contacts. When an idlecontact is found, an ener izing circuit is established for the relay C6 traced from battery through the winding of the motor magnet MM' its normal contact 186, conductor 18?, through the winding of the cut-off relay CO conductors 188 and 189, to ground at alternate contact 190 of the line relay LE The motor magnet MM is not energized over this circuit due to the resistance of cut-01f relay CO"; The cut-ofl' relay CO upon energizing opens its normal contacts 183, 18 1, opening the energizing circuit for the line relay LR The closing of the said alternate contacts 183 and 184 of the cut-off relay C0 of the switch K extends the line conductors to wipers 178, 179 and 180 which engage contacts of the selector or connector seized, as

described in connection with Fig. 1. The

line relay LE upon de-energization opens.

the initial energizing circuit for the cutoff relayv CO but the cut-cit relay CO being slow to release, the relay is held momentarily energized until a substitute energizcnt-ofi' relay CO through the winding of the saidcut-ofi' relay, conductor 187, normal contact 186 of the motor magnet MM and through the winding of the magnet MM to battery and ground. The cut-ofi' relay remains energized over this circuit until termination of conversation.

Assuming now that the called substation H is a called line, the. ground extending from the connector associated with the substation H extends over conductor 193,

7 through normal contact 194, through the winding of the motor magnet MM to battery and ground, and the opening of normal contacts 181 and 185 of the motor magnet MM removes the substation control of the line switch K.

Upon termination of conversation motor magnet lV[M 'of switch K restores to. normal, and assuming that. the Contacts with which the wipers 178, 179 and180 are engaging have been appropriated by another switch, a circuit will be immediately established for the motor. magnet MM from the now busy grounded contact 17 5, through the wiper 178, conductor 191., normal contact 192 of relay CO normal contact 186 of the motormagnet Mil/l through the winding of the. magnet MM to battery and ground.

The'magnet 'MM? upon operation steps'the wipers into engagement with the next set of contacts. The motor magnet MM upon energizing opens its interrupter contact 186,

allowing said magnet hit to de-energize,

and should the next set of contacts encouin tered now engagedbyt-he wipers be busy, another circuit is established for the motor magnet MM to step the wipers into engagement withthe next set of contacts. This stepping of the wipers is continued until an idle set of contacts are encountered.

Should the substation H be neither a calling nor a called subscriber, and assuming that the contacts engaged by the wipershave been appropriated by another switch, the contact 175 is grounded, this ground extending over conductor 191, to normal is permanently grounded, to provide full j preseleetion for the switch K, the ground.

encountered by the wiper -17 8 extends through thewiper 178, over conductor 191, to normal contact 192 of the cut-ofl relay 00 through the interrupter contact 186.

and the motor magnet. MM to battery and ground. The motor magnet MM thus steps the wipers from the normal home contacts engaged by the said wipers into engagement with the next set of contacts and the wipers continue to step ahead until an idle set of contacts are encountered. 1

When the switch is used on the strictly preselector basis the wiper 178 is always maintained in engagement with an idle trunk so that as soon as the subscriber removes his receiver at substation H, his line is immediately .eonneeted. to the idle trunk.

lit

The home contact of switch K, of course, could be connected through an interrupter to ground. I

WVhile I have shown a system of 100 capacity, it is to be understood that by inserting first selectors, the system may be in creased to a 1000 system, etc.

e What I claim as new and desire to secure by United States Letters Patent, is:

1. A telephone system including a" non numerical non-restoring I trunking switch having only three operating magnets one of which. is a motor magnet, subscriber-con trolled means for operating said motor mag,- net to cause said switch to connect the subscribers line to a trunk, subscriber-controlled means for operating said motor magnet without effecting operation of the other of saidinagnets to prevent said first subscriber from 6X61G1S1I1g a control over said switch and means for maintaining said switch always in engagement with a set of contacts connected to an idle trunk.

2. A telephone system including an automatic single. level non-restoring trunking switch having only three operating magnets,

so arranged that its wipers always remain in contact with an idle trunk unless the wipers of the switch are in one certain position. 3. An automatic non-restoring single level switch of the character described provided with bank contacts connected'to circuits, wipers for saidswitch always in engagement with contacts of said bank of contacts, and means for maintaining said wipers always in engagement with a set of contacts connected to an idle circuit unless the wipers I of the switch are in one certain position.

4t. A switch of the non-restor ng progressively movable single level type provided withineans to maintain the wipers of the switch in engagement with idle 'bank contacts unless the wipers ofthe switch are in one certain. position.

.5. A switch of the progressively movable n0n-rest0r1ng type provided with means for maintaining its wipers in engagement with idle contacts unless the wipers of the switch are in one certain positionr non-restoring switch provided with bank moving saidwipers when they are inengage mentwith'one set of said bank contacts even though the switch is not being used for'callingpurposes, and means for permitting the switch to remain; in engagement with am 6. An automatic progressively movable other set of bank contacts under all conditions except when the switch is used for calling purposes.

7. A system of the character described iiicluding a plurality of non-restoring switches arranged in a group and having accessto multiply connected link circuits, circuits so arranged that the switches of the group maintain their wipers in engagement with idle link circuits when the switches are idle, and whereby the switches do not maintain their wipers in engagement with idle circuits when the switches are idle and when the said wipers are in one certain position.

8. An automatic progressively movable non-restoring switch provided with bank contacts connected to connecting circuits, other bank contacts for said switch, circuit connections for maintaining the wipers of gage the said other contacts it remains there V with contacts connected to until the switch is used.

9. An automatic progressively movable non-restoring switch provided with bank contacts connected .to connecting circuits, other bankcontacts for said switch, circuit connections for maintaining the wipers of said switch when idle and in engagement with any of said first contacts in connection with an idle connecting circuit, and means whereby when the wipers of said switch engage said other contacts and the switch is idle the wipers thereof will be moved from engagement therewith and into engagement circuit.

10. A system of the character described provided with switches of the non-restoring type, bank contacts for said switches connected to link circuits, other bank contacts for said switches, means for maintaining the wipers of said switches when idle in engagement with contacts connected to an idle link circuit, and means formaintaining the wipers of said switches whenidle in engagement with idle link circu ts or n engage- 11161113 with said other contacts.

11. An automatic progressively movable switch of the non-restoring type that operan idle connecting with said auxiliary set of contacts until said engagement with said other contacts and into engagement with contacts connected to an idle link circuit. I

-14:.,A system of the character described including progressively movable non-restoring switches, multiply connected bank contacts for said switches connected to link circuits, other bank contacts for said switches,

means foralways maintaining the wipers of said switches when said switches are idle in connection with idle link circuits until said wipers engage said other bank contacts, andvnieansfor permitting said switches to maintain their wipers iii connection with said other bank'contacts until said switches are taken for use.

15. A system of the character described including progressively movable non-re'storing switches, multiply connected bank conftacts for said switches connected to link said I circuits, other bank contacts for switches, meansfor maintaining the wipers of said switches when said switches are idle whereby said switches maintain their wipers in engagement with said other bank contacts until taken for use, and means whereby said switches may'move their wipers 111'COIII1GQ131OI1 with idle link circuits, means to said other bank contacts and their wipers 1 remain there for a predetermined period of time, at which time thewipers areremoved from engagement with said bank contacts and into engagement "with contacts connected to an idle link circuit.

16. A system of the character described including progressively movable non-restoring switches, multiply connected bank contacts for'said switches connected to link cir- "cuits, other bankcontacts for said switches, means for vmaintaining the wipers of said home set of contacts for-said switch, means said normal or home set of contacts until for maintaining the wipers of said switches said switch is used for calling purposes.

when icllc in engagen'ient with contacts con- Signed by me at Chicago, in the county of 19 nected to an idle link circuit until said Cool; and State of Illinois, this 27 day of Wipers engage such normal or home set of January, 1921; c

contacts, and means for maintaining the r Wipers of said switches in engagement with LEROY D. KELLOGG. 

